1. Field of the Invention
The present invention relates to a mold temperature adjusting apparatus and method by which a change-over timing between a high temperature medium and a low temperature medium is appropriately adjusted so as to shorten a molding cycle time. The present invention also relates to a mold temperature control unit of the same concept.
2. Description of the Related Art
In an injection step of an injection molding machine, if a mold temperature is low, a molten resin that is injected makes contact with the mold while pressure in the mold is not elevated yet, so that a resin surface rapidly solidifies and a surface of a molded article often becomes coarse. This is liable to cause a problem that the molten resin is not sufficiently transferred onto a cavity surface of the mold. In order to avoid this problem, it is necessary to elevate the mold temperature so that solidification of the surface of the molten resin is delayed. On the other hand, once the resin is filled in the mold, it is preferable that the mold temperature is lowered so that cooling is expedited and the injection step cycle is shortened. In the recent molds, there are devised and provided various mold temperature adjusting apparatus and methods by which such mold temperature can be quickly elevated or lowered. However, as the mold generally has a large thermal capacity, if large amounts of high temperature medium and low temperature medium as heat medium fluids are alternately changed over to be supplied, it is necessary to devise a change-over means so that the high temperature medium and low temperature medium are not mixed with each other. Also, it is necessary to provide a high temperature medium recovery means so as to suppress a heat loss of the heat medium.
In a conventional heating/cooling change-over apparatus, a recovery tank exclusive for the high temperature medium and a recovery tank exclusive for the low temperature medium are provided. When a mold heating step is to be changed over to a mold cooling step, the high temperature medium remaining in a temperature adjusting passage in the mold is pushed out from the temperature adjusting passage by the low temperature medium newly supplied into the temperature adjusting passage to be recovered into the recovery tank exclusive for the high temperature medium. Also, when the mold cooling step is to be changed over to the mold heating step, the low temperature medium remaining in the temperature adjusting passage is pushed out from the temperature adjusting passage by the high temperature medium newly supplied into the temperature adjusting passage to be recovered into the recovery tank exclusive for the low temperature medium. This is disclosed in the Japanese laid-open patent application 1998-34657 as Patent Document 1, for example.
In another conventional example of a heating/cooling change-over apparatus and a mold heating/cooling change-over method, the number of the recovery tanks is reduced, whereby only the high temperature fluid is recovered so as to lessen the thermal energy loss. That is, there are provided a high temperature fluid passage system comprising a circulating passage, a pump transferring a fluid and a heater heating the fluid and also comprising an opening/closing valve enabling a change-over of the high temperature fluid passage system between a communicating state and a non-communicating state, a temperature adjusting passage (a fluid passage provided in a mold, a fluid supply and return passage), a recovery tank arranged in the high temperature fluid passage system and a discharge valve discharging the fluid stored in the recovery tank outside of the system. Thereby, when the mold cooling step is to be changed over to the mold heating step, the low temperature fluid remaining in the temperature adjusting passage is recovered into the recovery tank. Also, when the mold heating step is to be changed over to the mold cooling step, the high temperature fluid remaining in the temperature adjusting passage is recovered into the recovery tank. This is disclosed in the Japanese laid-open patent application 2002-210740 as Patent Document 2, for example.
In the heating/cooling change-over apparatus of the above-mentioned Patent Document 1, there are needed two recovery tanks on the high temperature side and the low temperature side as the fluid medium recovery tank. Also, the high temperature medium is left as it is in the recovery tank in the mold cooling step. Hence, the temperature is considerably reduced by a radiation and when this high temperature medium is returned into the high temperature medium passage, it is mixed with a high temperature medium of which temperature has been adjusted to an appropriate high temperature and there arises a problem that the temperature is reduced.
Also, in the heating/cooling change-over apparatus and mold heating/cooling change-over method of the above-mentioned Patent Document 2, while the low temperature fluid recovered into the recovery tank is discharged out of the system, the recovery tank is cooled by the recovery of the low temperature fluid so that the recovered high temperature fluid also is cooled in the recovery tank. Thus, when this recovered high temperature fluid is recovered into the high temperature fluid passage system, the temperature of the high temperature fluid is reduced and there arises a problem that the high temperature fluid is to be re-heated in the high temperature fluid passage system so that a temperature adjustment is carried out.